In large parts of the world the fresh water resources are limited and drinking water therefore has to be produced from brackish water or sea water. The most common water purification plants are evaporation/condensation processes in which the requisite energy is produced by burning cheap natural gas (in the Gulf region) or more commonly, by harnessing solar energy. In many regions there is a great need for simple, efficient and low-cost equipment for the desalination of sea water.
A number of such plants and devices for desalination and purification of drinking water which employ solar energy are previously known.
DE 2503251 makes known a device for producing drinking water from polluted or saline water with the aid of solar energy. This evaporator consists of a basin with a roof in the form of an inverted V, which can be penetrated by solar energy. In the lower end of the inclined roof there is a run-off channel which receives water that has condensed on the inside of the roof.
DE 3501396 A describes a similar device having a basin and a glass roof in the form of an inverted V. In the lower end of the roof there is a collecting channel for water which has condensed on the inside of the roof.
DE 2650482 describes a device consisting of a basin and a sloping glass roof, wherein the glass roof is cooled in order to enhance the condensation.
International Patent Application WO 91/04228 makes known a method and device for producing drinking water from polluted water with the aid of solar energy, consisting of a construction having a plurality of chambers or sections, of which one chamber or section is an evaporation chamber and a second section is a condensation chamber. Swedish Published Patent Application 46213 makes known a transportable device for producing fresh water by desalting sea water with the aid of solar energy. The device includes a casing having at least one transparent portion and a collecting channel for fresh water. In the bottom of the device there is provided a solar energy absorber having ducts for cooling the absorber with the aid of a coolant. The coolant flows in a closed circuit and is used to heat the incoming sea water.
U.S. Pat. No. 4,187,151 describes a floating desalination plant. A bottom having a preferably transparent or translucent chamber floats on the surface of the sea. Waves cause the chamber to expand and contract so that air is drawn into the chamber. The moist air exiting the chamber is conducted to a condensation and collecting tank below the sea surface.
There are also known a number of devices which use reverse osmosis for producing fresh water from sea water. As examples of publications which describe this, reference may be made to U.S. Pat. Nos. 4,076,626, 4,452,696 and 4,770,775.
One disadvantage of the known devices is that they are relatively bulky and relatively stringent requirements must be met with respect to periodic maintenance.
Another disadvantage of these known devices is that they are relatively inefficient, since most of the solutions are based on a more or less closed chamber, where the water vapor is condensed on the surface of the chamber.